Accept this answer as the solution please. I had the same problem on Debian and none of the other parameter naming and domain\username tricks in the other answers solved it. Thanks for it!
–
Daniel DinnyesOct 7 '14 at 15:38

I know the credentials are correct and the servers can communicate, as the smbclient can connect
–
Dr GorbMay 17 '13 at 11:24

@DrGorb: That's not actually what I said to chcek though.
–
IainMay 17 '13 at 11:28

what I meant is that the credentials are correct and written correctly and that they are accepted by the Windows server and that the Linux server can send them. If I enter wrong credentials I get the same error though
–
Dr GorbMay 17 '13 at 11:44

@DrGorb: So it won't hurt to put quotes around them just to check will it ?
–
IainMay 17 '13 at 11:46

tried with single and double quotes: same result
–
Dr GorbMay 17 '13 at 12:18